Add JS docs on all exported items

[joelgallant]

For usage in Node.js, it's useful for intellisense.

• [x] @app-config/core
• [ ] @app-config/config
• [ ] @app-config/extension-utils
• [ ] @app-config/node
• [ ] @app-config/schema
• [ ] @app-config/meta
• [ ] @app-config/settings
• [ ] @app-config/webpack
• [ ] @app-config/logging
• [ ] @app-config/generate
• [ ] @app-config/extensions
• [ ] @app-config/encryption
• [x] @app-config/main
• [ ] @app-config/utils